Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with agraphical user interface showing my new design.

The outermost broken line illustrates the border of the display screenand forms no part of the claimed design. The remaining broken linesshown within the Graphical User Interface, including the broken lineswithin the graphs and charts and the broken line text and indicia, formno part of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.